Abstract: The metal-semiconductor-metal photodetectors (MSM-PDs) have received great attention in areas of optical fiber communication, sensing, missile guidance, etc., due to their inherent merits of high speed, high responsitivity, and easy integration. This review focused on MSM PDs with the semiconductor layer made of inorganic materials. Firstly, the basic structures of MSM-PDs was introduced, including the planar and vertical configurations. Then, the working principles of MSM-PDs were introduced. In addition to the common photoconductive and Schottky principles, the principle of hot carrier photodetectors with the metal layer as the light absorbing part was also introduced. Subsequently, the research progresses of MSM-PDs made of inorganic materials such as GaAs, InGaAs, Si/Ge was described in detail. Additionally, the research progress of using metallic micro/nano structures to extend the response of wide energy band semiconductor based MSM-PDs in infrared wavelength range was presented. Finally, the full text was summarized and the future development of MSM-PDs was prospected.